The group of four, known as The National Democratic Opposition Parties in Bahrain, told journalists at a news conference Saturday that they are not taking part in the elections until a "clear political" agreement that reflects the will of the people is reached.

The largest opposition party, Al Wifaq, withdrew its 18 members from parliament in 2011 after the Sunni monarchy moved to crush protests by the Gulf Arab country's Shiite majority. Protesters are demanding a greater political voice and equal rights.

There are 80 seats total in Bahrain's parliament, divided equally between the upper and lower chambers. Elections are held every four years. The last time the opposition boycotted was in 2002.